The Pinnacles National Monument is located in the Gabilan Range between the Salinas and San Benito Valleys in central California. The rock visible here is volcanic breccia that was eroded from siliceous volcanoes that erupted about 22-23 million years ago. Similar siliceous volcanic rocks occur at Neenach California, about 315 km to the south but on the other (eastern) side of the San Andreas Fault. Together, these volcanic rocks, which crop out about 315 km apart, provided one of the earliest estimates of long-term slip rates for the San Andreas Fault, about 14 km/my, or 14 mm/y.
The rocks that form the iconic pinnacles of the park are volcanic breccias that represent material that has shed off of a large siliceous volcano. These breccias were strongly cemented to create resistant, cliff-forming rock unit. Joints formed in these breccias which helped formed the iconic pinnacles that give the park its name. Most of the joints are oriented vertically, but many can be seen in this image dipping shallowly to the left, especially along the shores of the reservoir and on the large rock face on the right side of the image.
The Pinnacles is part of the California Condor Recovery Program. Thirty four free-flying condors are tracked by park personnel. This population of condors was re-introduced into this area in the early 2000’s. More information: http://www.nps.gov/pinn/naturescience/condors.htm
The strong resistant rocks of The Pinnacles have long been favorites of rock climbers. Rock climbing bolts and slings are a permanent part of many of the cliffs within the park. The rock wall in right center of the image is a popular climb.
Another large scale-panorama of The Pinnacles is here:
http://www.gigapan.org/gigapans/97797
A close-up of the volcanic breccia of a large rock wall called The Monument is here:
http://www.gigapan.org/gigapans/97795
Close-ups of the volcanic breccia are here:
http://zoom.it/wmFj
http://zoom.it/WpbI
http://zoom.it/LBjJ
http://zoom.it/GqIv
http://zoom.it/NO3W
Climbers and ropes provide scale. Information about climbing routes is here:
http://www.rockclimbing.com/routes/North_America/United_States/California/Central_California_Coast/Pinnacles_National_Monument/Monolith__The/
A good 2008 summary of the geology of the park is here
http://sfnps.org/download_product/1381/0
The classic 1936Phillip Andrews treatise on the geology of the Pinnacles is here
http://www.cr.nps.gov/history/online_books/geology/publications/state/ca/uc-24-1/